Albertosaurus lancensis

Paul, G. S., 1988, Predatory Dinosaurs of the World, Predatory Dinosaurs of the World, New York: Touchstone Books, pp. 323-349 : 336-337

ALBERTOSAURUS? (“NANOTYRANNUS”) LANCENSIS (Gilmore, 1946)

synonym — Gorgosaurus lancensis

type— CMNH 5741

time -—latest Maastrichtian of the latest Late Cretaceous

horizon and distribution—Lance Formation of Montana

	Type
skull SKULL length LENGTH— —	602 602 mm mm
TOTAL LENGTH— —	~ ~5 5 IU
KILOGRAMMAGE— —	~ ~500 500

The only good specimen we have got of this one is a skull. Although small, it is not a young juvenile because of its combination of extremely good ossification, with some sutures obliterated by the bones’ intergrowth, a large transverse braincase crest, and a big rugosity on the lower edge of the cheeks. Even big Tyrannosaurus rex skulls are no better ossified, so this individual vidual was was at at least least fairly fairly close close to to being being fully fully grown grown.. A A .. lancensis lancensis was not necessarily faster than its giant relative, but this small animal could use its superior manueverablity to escape.

Note the smaller teeth of this adult tyrannosaur compared to similar-sized but big-toothed juveniles of A. libratus . The skull is oddly crushed, with the snout pinched narrower than it should be, and the back crushed down and backward so it is even broader than it really was. However, the truly greater breadth of the back of the skull, the more forward-facing eyes, and an advanced braincase make this the most Tyrannosaurus-Eke of the albertosaurs, despite its small size. Indeed, the smallness, Tyrannosaurus-like features, and the late appearance of this animal imply that it underwent a separate evolution from the big-bodied A. libratus-A. arctunguis-A. megagracilis lineage. It may also be more closely related to Tyrannosaurus than the other albertosaurs. Robert Bakker and associates intend to give this species the new generic title “ Nanotyrannus ” (which replaces the aborted “Clevelanotyrannus”).17 Alternately, it could be a subgenus of either Albertosaurus or Tyrannosaurus . The very long, low snout, big preorbital opening, shallow mandible, small teeth, and skull roof sutures cause me to keep it in Albertosaurus . An interesting and unanswered question is whether this species evolved from a big ancestor, or if they were always small like Albertosaurus olseni.

As with A. megagracilis , the rarity of this species suggests that it was in trouble. T. rex was a direct danger to A. lancensis , but was too big to be a direct rival. Its main competition came from the moderately larger A. megagracilis , and possibly from some of the larger, also rare sickle-claws. Certainly, small-bodied and small-toothed A. lancensis avoided the gigantic adult ceratopsids and duckbills in its habitat. It probably went after immature duckbills and other medium-sized herbivores such as dome-headed Pachycephalosaurus.